The AAI Corporation was founded in 1950, as Aircraft Armaments, Inc., and has long been involved in advanced firearms design, taking part in a number of the US military’s previous small arms programs. Throughout the Cold war AAI was involved in the US Army’s search for a new advanced infantry weapon system. Before we examine the AAI ACR, it is important to understand the context in which it evolved.

The Special Purpose Individual Weapon (SPIW) program, an off-shoot of Project SALVO began in the early 1950s and ran until the late 1960s. During the SPIW program AAI developed a series of designs, including an entire family of weapons, which used flechette technology. These culminated with the XM19 rifle, or SFR – Serial Flechette Rifle. The XM19 represented the pinnacle of over a decade of flechette technology development, however, the end of the US war in Vietnam saw the need for SPIW disappear and the program was wound down.

AAI SPIW family of weapons from the early 1960s (Reproduced in Stevens & Ezell’s SPIW Deadliest Weapon)

In the early 1970s SPIW essentially morphed into the Future Rifle Program, but with the end of US involvement in Vietnam, this also proved a failure. During the early 1980s the US Army awarded development contracts to both AAI and Heckler & Koch to develop caseless ammunition and a weapon system capable of firing it. While H&K G11 is no doubt the better known of the two weapons, AAI’s Caseless Weapon, while a move away from flechette technology, was also an interesting design.

Firing a variety of ammunition the AAI design was capable of firing a high cyclic rate 3-round burst at 1600-1800rpm. The ACR program summary report noted that the AAI Caseless project was feasible and only lacked development funding to make it a reality, as the design was much simpler than the G11.

AAI were one of six companies to respond to the ACR program’s Request for Proposals, released in September 1985. AAI’s ACR was an evolution of the earlier SFR/XM19 rifle. The weapon AAI submitted was gas-operated, fed from a 30-round box magazine, and fired a brass cased flechette round in either single shot or a high cyclic rate three round bust – fired at a cyclic rate of ~1800rpm.

AAI’s ACR fired from a closed bolt and used a muzzle device to reduce muzzle climb during burst firing. The 1990 ACR Program Summary report explains how the rifle’s gas system worked:

“…incorporate an ‘entrapped gas’ operating system. Gun gases enter a cylinder, drive a piston to power the system, and prevent any leakage of propellant gases and residues into the other mechanism parts.”

AAI developed a polymer saboted steel 10.2 gr ‘sub-calibre’ flechette which fitted within a standard M855 brass case. As a result the rifle used a proprietary magazine to avoid the accidental chambering of conventional 5.56x45mm rounds. The flechette rounds had a muzzle velocity of 4,600 ft/s with propellant produced by the Olin Corporation.

An AAI Corporation ACR marked serial number 20 (Matthew Moss)

The rifle was designed to mount a quick detachable 4x optic and also had a white-highlighted shotgun-style rib sight along the barrel to aid snap shooting. The rifle was one of the longest entries with an overall length of 40 inches or 101.6cm. Interestingly, rather than a push-button magazine release, AAI opted for a large paddle release.

The fore-end of the AAI ACR, note the front sight post and muzzle device which reduced muzzle climb during burst firing (Matthew Moss)

AAI’s rifle borrowed some of its external ergonomic characteristics from the M16A2, then in service. With a moulded polymer pistol grip and butt, forming part of the lower receiver, shaped to mimic the M16’s. It also utilised the M16’s sling loops and butt plate.

According to the ACR program summary the AAI entry proved to be a “mature design which performed in a reliable fashion” during the field trials. It was regarded as a weapon with known reliability with a flechette round superior to the Steyr, the other flechette-based entry.

Close up of the right-side of the AAI ACR, note the ejection port and moulded plastic case deflector, selector level, paddle magazine release and sight mount (Matthew Moss)

Today, AAI continue to develop both small arms and other defence technologies. Now a part of Textron, they are currently involved in the US Army’s Lightweight Small Arms Technologies (LSAT) program.

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